instructions): Chronic sleep disturbance is reported by nearly 50% of older adults. The high prevalence of insomnia in older adults is likely due to an interaction of age-related changes in sleep and circadian regulation, chronic illnesses and late life stressors. Recent evidence suggests that poor health contributes to poor sleep, but poor sleep can also increase the risk for poor health. Evidence from our group shows that sleep loss may promote the development or increase the severity of age-related cardio-metabolic disease. While many studies have confirmed the link between short sleep duration and cardio-metabolic disease, emerging evidence supports a relationship between insomnia symptoms and risk for cardiovascular disease. However, little is known of the impact of insomnia or its specific sleep characteristics on cardio-metabolic health in older adults. In the present study, we propose to examine in detail the relationship between sleep characteristics with cardio-metabolic risk factors in older adults with chronic insomnia. A total of 120 older adults with chronic insomnia and controls will be recruited from the Chicago Heart Association Detection Project in Industry cohort. This collaboration represents a unique and cost efficient opportunity to study the relationship between insomnia and cardio-metabolic risk factors in a large group of community based older adults ages 65-80 years of age. The overall aim of this project is to define the sleep, circadian and cardio- metabolic phenotypes of common age-related insomnia subtypes. Objective and self reported measures of nocturnal sleep, daytime sleepiness, circadian rhythm, metabolism, inflammation, and autonomic function will be assessed in older adults with chronic insomnia and compared to age, gender, race and BMI matched controls without insomnia. The specific aims are: 1) Assess whether levels of cardio-metabolic risk factors are higher in older adults with chronic insomnia than in their counterparts without insomnia; 2) Determine the role of each of the major sleep characteristics: total sleep time, sleep efficiency, latency to persistent sleep, sleep fragmentation, minutes of slow wave sleep, minutes of REM sleep, slow wave activity and high frequency activity, and daytime sleepiness on cardio-metabolic function in older adults with and without chronic insomnia; and 3) Determine the contribution of circadian phase and amplitude to the relationship between insomnia and cardio-metabolic disease risk factors. The results of the proposed study will greatly improve our understanding of the impact of insomnia and the role of specific sleep and wake characteristics on cardio-metabolic disease risk markers and daytime function in older adults. RELEVANCE (See instructions): The proposed study has important implications for public health. If chronic insomnia in older adults is associated with elevated cardio-metabolic risk factors, it would strongly underscore the importance of identifying and treating insomnia in older adults. Furthermore, these results can provide the basis for personalized approaches to the treatment of insomnia as well as the prevention of common age associated co-morbid medical and psychiatric conditions.